Preformed Particle Gel (PPG) for Conformance Control Missouri Energy Summit 2009 Preformed Particle Gel (PPG) for Conformance Control Baojun Bai, Yongfu Wu Petroleum Engineering Missouri University of Science and Technology March 23, 2009

Outline Oil Production Mechanisms Enhanced Oil Recovery (EOR) Targets Preformed Particle Gel (PPG) for Conformance Control Gel Treatments Advantage of PPG Treatments Enhanced Oil Recovery Mechanisms Applications Future Research Summary

Oil Production Processes Enhanced Oil Recovery (EOR) is a term applied to methods used for recovering oil from a petroleum reservoir beyond that recoverable by primary and secondary methods. Primary recovery normally refers to production using the energy inherent in the reservoir from gas under pressure or a natural water drive. Secondary recovery usually refers to injection of water or waterflooding. Thus, Enhanced Oil Recovery is often synonymous with tertiary recovery. Improved Oil Recovery (IOR) and Advanced Oil Recovery (AOR) have similar meaning, except they also apply to primary and secondary methods, and sometimes EOR methods can be used earlier in the sequence. At or before the time these drawings were prepared, waterflooding was considered as Enhanced Oil Recovery, but now EOR is generally considered to follow waterflooding. Four groups of methods - thermal recovery, gas miscible recovery, chemical flooding and microbial flooding - are included in this collection. Twelve EOR methods and two production technologies are described and illustrated in this collection. The thermal recovery methods are steamflooding, cyclic steam stimulation and in situ combustion. The gas miscible recovery methods are carbon dioxide flooding, cyclic carbon dioxide stimulation, nitrogen flooding and nitrogen-CO2 flooding. The chemical flooding methods are polymer flooding (including polymer gels), micellar-polymer flooding, and alkaline flooding. Microbial EOR methods include microbial flooding and cyclic microbial recovery. The production technologies are improved drilling technology and hydraulic fracturing. The OIL PRODUCTION illustration (with figures updated below) indicates the effect of EOR on production of the 568 billion barrels of oil that has been discovered in the United States. It is estimated that an additional 67 billion barrels of oil have not been discovered (total 635 billion barrels in the U.S.) The EOR target is 200 billion barrels of the 377 billion barrels of the remaining discovered resource that is producible with EOR. (Note that the illustration, drawn in the 1980’s, shows a recovery range of 4-1 1 % for EOR; the current figure, depending on the method used, ranges from 5-30%.)

Oil Recovery Mechanisms

EOR Targets EOR Potential in the U.S.A Original Oil in Place in USA: 649 Billion Barrels

EOR Potential in the World

The Four Key Issues to be Resolved to Maximize Oil Recovery Why cannot oil recovery be 100%? There are four reasons. The first reason is some residual oil (like oil drop/oil attached on pore surface) is left in the pores of water/gas flooded area. Secondly, many reservoirs have higher oil viscosity than displacing fluids, this will cause the fingering of injected fluid through oil. Thirdly, all reservoirs are heterogenous. This will cause injected water preferently flow through high permeability zones while the flow of oil in low permeability zones is hambered and cannot be recovered. Fourthly, many reservoirs have natural fractures, especially carbonate reservoirs. The fracture system cause carbonate reservoir recovery usually below 20%.

Preformed Particle Gel (PPG) for Conformance Control

What is Preformed Particle Gel (PPG) Preformed particle gel, also called PPG, is dried crosslinked polyacrylamide powder. When it contacts with water, It can swell several to a few hundred times of its original size. Like this pictures, here is dried PPG paticle here, when we pour water into the test-tube, the particle will swell to those much. So PPG is a kind of super absorbent polymer. (a) Before swelling (b) After swelling Cross-linked polyacrylamide powder SUPER ABSORBENT POLYMER

Why Gel Treatment Excess water production is the most serious problem to reduce oil production as oilfields are maturing. Improved sweep efficiency has become the most important target to improve oil recovery. Gel Treatments are often the best choice to mitigate channeling through fractures and super-K streaks

Gelant (polymer/monomer+crosslinker What is Gel? Gelant (polymer/monomer+crosslinker +additives) Gel Gel is a kind of crosslinked polymer. Before gelation, it is a liquid formulation, composed of several compositions, lke polymer, crosslinker and some additives. The liquid formulation is called gelant. At some conditions, such as temperature increase, pH change, the gelant can crosslink to form gel. Gel strength can be controlled by its gelant compositions and surrounded conditions, it can be weak,liking flowing gel, or very rigid, like rubber.

Gel Treatment to Block/Reduce Water Flow through High Permeability Zone/Streak Near Wellbore Treatment (no crossflow) In-depth Gel Treatment (thick heterogenous layer with crossflow) As I mentioned, The main purpose of gel treatments is to reduce excess water production from high permeability zones and increase oil production from low permeability zone by injecting gel. If the excess water is caused by reservoir problems, usually, there are two types of gel treatments, near well bore treatment and in-depth gel treatment. If no crossflow between low permeablity and high permeability zones, a small amount of gel can be injected into nearwellbore from an injection well or a production well. For injection well, like this carton, once gel is placed in high permeability zone, the permeablity in this zone will be reduced, more followed water will penetrate into low permeabilty zone than ever, so the injection profile is controlled. If gel treatment in a production well, like this carton, the gel is placed nearwellbore of the production well, the reduced permeability will limit water production from the high permeability zone, so more oil can produce from low permeabibility zone,which will result in reduced water cut and improved oil production. If there is a crossflow between layer, in-depth gel treatment is required. Usually gel is injected from an injection well rather than a production well for in-depth treatment.the large volume gel placed in high permeability zone will divert followed water to low permeabilty zone to displace the remaining oil KL Kh Gel

Gels Used for Conformance Control In-situ gel systems: Gelant is injected into formation and gel is formed under reservoir conditions after placement. Gelation occurs in the reservoir. Preformed gel systems: gel is formed in surface facilities before injection, then gel is injected into reservoirs. No gelation occurs in reservoir.

A Newer Trend in Gel Treatment is Using Preformed Gels Inherent disadvantages of In-Situ Gel Crosslinking reactions are strongly affected by Shear by pump, wellbore and porous media Adsorption and chromatography of chemical compositions Dilution of formation water Possible damage on unswept low permeability oil zone of in-situ gel

Current Preformed Gel Systems Preformed Bulk Gel: Dr. Seright/NMT, Robert Sydansk Micro Particle Gel: µm-sized particle by Zaitoun et al/IFP. One application in a gas storage well Bright Water®: Nano particle by Chevron, BP and Nalco Ten plus well pilot tests. Preformed Particle Gel: mm-sized Grained particle, Bai et al, bout 2,000 treatments

PPG Products Size Adjustable: um-mm Swelling Ratio: 30200 times original Salt Resistance: All salt types and concentrations are acceptable Temperature Resistance: High, to 110 ºC Long-term Stability: more than 1 year below 110 ºC.

EOR Mechanisms of PPG Treatment Oil Recovery ER=ED×EA×EV ER=Recovery Efficiency EV=Vertical Sweep Efficiency EA=Areal Sweep Efficiency Biggest Impact – Selective Plugging ED=Displacement Efficiency Some Effect

Experimental Results of Parallel Core Flooding (Vertical Heterogeneity Model) No. Permeability (Darcy) Split of Flow (percent) Oil Recovery ( 98% water cut) Total Oil Recovery Before (%) after (%) before (%) after (%)） After (%) S1 8.23 91 20 70 75 46.8  64.9 0.54 9 80 22 54 KL=0.54 D Kh=8.23 D

Areal Sweep Efficiency Improvement MICROMODEL DEMONSTRATION Areal Sweep Efficiency Improvement water glass PPG oil drop 3cm a. Remaining oil distribution in main stream Before PPG Inj. After PPG Inj. Areal heterogeneity is caused by reservoir heterogeneity or pressure distribution. This visual micromodel experiment shows why PPG can improve areal sweep efficiency. It is a five spot well group unit. Before PPG treatment, water was injected to displace oil till no more oil produced. You can see, at that time, in the mainstream almost no remaining oil existed due to its high pressure gradient, but a lot of oil was left in the corner. After PPG treatment, PPG blocked the mainstream, and followed water was diverted to the corner to displace its remaining oil. More water diverted to corner after PPG injection b. Oil distribution at corner – Now lower

Increased Oil Recovery Experimental Results from Single Sandpack Demonstrates Improved Displacement Efficiency Core No. K (D) PPG Size (mesh) Swi (%) Oil Recovery1 Oil Recovery2 Increased Oil Recovery No1 22.5 250 22.4 62 73 11 No2 20.6 160 23.2 64 74 10 “1” refers to oil recovery from water flood before PPG injection “2” refers to total oil recovery from both water flood and PPG treatments Single sandpack experiments were performed to show if PPG can improve displacement efficiency of oil. We assume single sandpack is a homogenous core. As shown in the table, PPG can improve oil recovery about 10%, which is a displacement effect.

Field Applications About 2000 treatments so far Reservoirs: Naturally fractured reservoirs Reservoirs without initial or hydraulic fractures. Temperature: 30~110 ºC Salinity: 2,900 ~ 300,000 mg/L PPG amount: 1, 000 ~120,000 lbs/well, commonly 15,000-40,000 lbs/well. Typically

First pilot in Zhongyuan, SINOPEC Treatment Results Increased Oil 29,151 bbl Oil incr. per PPG 0.3 bbl of oil per lbs of PPG The performance of center producer connected with W51-75 and P-72

Future Research Swollen particle transport mechanisms through high permeability zones and fractures. Development of nano- or micro-sized swelling rate controllable particle gel. Combination of PPG treatment and other EOR methods to enhance overall oil recovery.

Summary Up to 65% reserve is remained after waterflood. EOR should be considered, and can extract up to additional 25% OOIP. PPG treatment overcome the distinct disadvantage of traditional in-situ gel treatments. PPG treatment is a cost-effective method to improve oil recovery and reduce water production

Acknowledge Financial Support from Research Partnership to Secure Energy for America (RPSEA) under DOE contract Missouri University of Science and Technology